Air filter



FIG. 1 is a front top perspective view of an air filter according to thenew design;

FIG. 2 is a rear bottom perspective view thereof;

FIG. 3 is a front elevation view thereof;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a bottom plan view thereof.

The broken lines in the drawings show portions of the air filter thatform no part of the claimed design.

CLAIM The ornamental design for an air filter, as shown and described.